The long-term goal of the proposed project is the development of a desktop circular array Small Animal Ultrasound Tomography System (SAUTS) to produce high-resolution cross-sectional diagnostic images of mice and other small laboratory animals. The SAUTS images will look familiar to the radiologist, resembling those produced by Micro-CT or MRI. They will be easy to interpret, as the circular tomographic approach alleviates most of the artifacts associated with conventional ultrasound images. The effects of the animal?s heartbeat, breathing, and motion on the image quality will be minimized by resorting to very high recording frame rates. The ability to map multiple elastic parameters, e.g. sound speed, reflectivity and attenuation can be used to fully characterize the biomechanical properties of internal organs and tumors. SAUTS will simplify the routine examination process. In some cases, it will be even possible to hold the animal by hand while pressing a foot pedal to take an instant image. To scan a set of multiple slices, a comfortable and stress-free mouse holder will be supplied. Compared to other cross sectional imaging modalities, SAUTS will be relatively inexpensive, portable, and suitable for daily repeated testing without harming animals and, as a result, eliminating any possible influence on the outcome of biomedical and pharmaceutical experiments being monitored. The proposed Phase I project has the following Specific Aims: (1) To prove the feasibility of in- house manufacturing of a ring array probe with embedded signal conditioning electronics and to test its performance on laboratory phantoms; (2) To develop a realistic top-level design of an affordable high-resolution imaging system. These Aims will be achieved by (a) designing, building, and optimizing a 16-channel segment of a low-noise ultrasound probe; (b) Assembling a 192-element circular array from segments and connecting it to the existing phased array controller; (c) Implementing data acquisition and image reconstruction software and verifying performance on phantoms; (d) Turning the ring array by small angular increments and compounding the data to study the expected resolution at higher channel counts; (d) Preparing Phase II development plan. Successful completion of these steps will allow building a practical SAUTS prototype with large channel count and high frame rate in Phase II. Once commercialized, SAUTS will be used in biomedical and pharmaceutical research labs to monitor anatomical changes in vascular, digestive, respiratory, reproductive, and other systems of small animals, including growth/shrinkage of tumors in response to new drugs and therapies.